This invention relates to a heavy duty pneumatic radial tire, and more particularly to tires suitable for use in vehicles such as trucks, buses and the like, and particularly it relates to a heavy duty pneumatic radial tire in which an organic fiber cord layer is used in a bead portion of the tire used under severe conditions of load, running speed and the like as a reinforcing layer effective for the bead portion to improve a bead portion durability.
In the heavy duty pneumatic radial tire suitable for use in trucks, buses and the like, it is common to reuse a base tire for recapping when a tread rubber reaches a service limit in the wear because it is not desirable to use a new tire only once. Referring to FIG. 16, illustrating a section of a main part of the conventional tire inclusive of a bead portion, there is often observed a case of causing a long and large crack or a separation failure accompanied with the growth of the crack in an end 4te of a turnup portion 4t of a carcass 4 or an outer end 6e of a rubberized steel cord layer (generally called a wire chafer) 6 as a reinforcing layer for a bead portion 1 among members constituting the bead portion 1. The used tire having such defects is unsuitable as a base tire and it is obliged to give up recapping thereof. When the service conditions are very severe, the aforementioned crack or separation failure is caused even in the new tire on the way of the service life.
The aforementioned long crack or separation failure in an end portion such as end 4te, end 6e or the like results from the concentration of large strain in such end portion. Referring to FIG. 17 showing a section of another conventional tire, in order to eliminate this strain, there is widely used means where one or more organic fiber cord layers, two layers in the illustrated embodiment, for example, nylon cord layer 15 (15-1, 15-2) generally called a nylon chafer are arranged outside the turnup portion 4t of the carcass 4 alone in case of FIG. 16 or together with the steel cord layer 6 as the reinforcing layer in the case of FIG. 18 and adjacent thereto at a height sufficiently covering the above end portion in a radial direction of the tire.
However, the application or addition of the organic fiber cord layer 15 does not develop an effect to an intended extent and reasons thereof are investigated to elucidate the following facts.
That is, as a part of the two organic fiber cord layers 15-1, 15-2 (see FIG. 17, FIG. 18) is perspectively shown in FIG. 19 showing a half lower-side of a tire running under loading at a zone ranging from a leading edge of a contact patch to a trailing edge thereof, cords CR (upward to the right in the figure) and cords CL (upward to the left in the figure) of the organic fiber cord layers 15-1, 15-2 are arranged so as to cross with each other between the layers in a bead portion 1 corresponding to a ground contact region of the tire tread rotating under a given air pressure and under loading, so that even in either case of arrangements upward to the left and the right, the cords have to be always subjected to compression deformation at the leading side or the trailing edge of the contact patch.
Although detailed reasons of always causing the compression deformation will be described later, the degree of compression deformation becomes higher when the traction force and braking force are further applied to the tire. When an axial compression force is applied to the cord in the organic fiber cord layer 15, the modulus of the organic fiber cord becomes very low to the axial compression, so that the rigidity required for developing a stress mitigating function of the organic fiber cord layer 15 naturally intended to the turnup end 4te of the carcass 4 or the end 6e of the reinforcing layer 6 is largely diminished. According to experiments, a ratio of axial compression modulus to tensile modulus in the organic fiber cord layer embedded in rubber is only about 0.1.
And also, it has been confirmed that cracking failure is caused in an end portion of the organic fiber cord layer 15 toward the outside of the tire. As a result of an investigation on the cause of the cracking failure, it is elucidated to be caused by a large tensile strain applied to rubber in the vicinity of the end 15e of the organic fiber cord layer 15 toward the outside of the tire. That is, air pressure filled in the heavy duty pneumatic radial tire mainly used in truck and bus is as high as 7.00xcx9c9.00 kgf/cm2, for example, at room temperature and is further increased by a rising of tire temperature accompanied with the running of the vehicle. As shown in FIG. 18, a large tension T is applied to the carcass 4 by a higher internal pressure, and the large tension T produces pulling forces a, b of arrow direction in not only the turnup portion 4t of the carcass 4, but also the bead portion reinforcing layer 6 and the organic fiber cord layer 15 and hence the turnup portion 4t, bead portion reinforcing layer 6 and organic fiber cord layer 15 are forcibly displaced in the acting direction of the pulling forces a, b. Such a forced displacement particularly causes a large tensile strain e in rubber near to the end 15e of the organic fiber cord layer 15. The tensile strain e is further increased by bending deformation of the bead portion 1 under loading shown by a phantom line. Consequently, a fatigue crack is created in rubber near to the end 15e of the organic fiber cord layer 15 by repetitive action of strain amplitude of the tensile strain e accompanied with the rotation under loading, which grows to finally cause the separation failure.
In addition, it is strongly demanded to form a lower section profile of radial ply tires for recent trucks and buses, from which it tends to increase low-section tires. In the low-section tire used under heavy load, the deformation of the bead portion 1 is particularly increased and the strain amplitude quantity of the tensile strain e is considerably increased, so that there is high-lighted cracking failure or separation failure in the end 15e of the organic fiber cord layer 15 located toward the outside of the tire, which has hardly been observed in the conventional tire. This type of the failure is a recent tendency and an effective improving countermeasure does not exist at the present time.
It is, therefore, an object of the invention to provide a heavy duty pneumatic radial tire in which the organic fiber cord layer advantageously develops the rigidity as a stress mitigating layer to the end of the turnup portion of the carcass and the end of the bead portion reinforcing layer made of the steel cord layer extending over the turnup end outward in the radial direction of the tire and also the resistance to cracking in the end of the organic fiber cord layer is largely improved even in a tire having a small aspect ratio to considerably improve the bead portion durability and recapping property as compared with the conventional tire.
In order to achieve the above object, a first aspect of the invention lies in a heavy duty pneumatic radial tire comprising a carcass of at least one rubberized cord ply of radial arrangement toroidally extending between a pair of bead core embedded in bead portions and wound around the bead core from inside of the tire toward outside to form a turnup portion, and at least one rubberized organic fiber cord layer extending outside the turnup portion over an end of the turnup portion outward in a radial direction of the tire, in which the organic fiber cord layer is arranged so as to extend from a position near to an outside of the bead core over the end of the turnup portion toward the outside of the tire and spread apart to the turnup portion.
In a preferable embodiment of the first aspect of the invention, the organic fiber cord layer has a first bent portion acutely bending toward the outside of the tire with respect to a winding direction of the turnup portion extending outward from the position near to the outside of the bead core in the radial direction, and a bending angle xcex1 of the first bent portion with respect to the winding direction of the turnup portion at a radial section of the tire is within a range of 15xcx9c60xc2x0.
In another preferable embodiment of the first aspect of the invention, a bead portion reinforcing layer made of a rubberized steel cord layer is disposed between the turnup portion of the carcass and the organic fiber cord layer and an outer end of the reinforcing layer in the radial direction of the tire locates inward from the end of the turnup portion in the radial direction of the tire.
In the other preferable embodiment of the first aspect of the inv$ention, an end of the first bent portion of the organic fiber cord layer is an outermost end in the radial direction of the tire.
In a still further preferable embodiment of the first aspect of the invention, the organic fiber cord layer has the first bent portion and a second bent portion again bending from an end of the first bent portion toward an inside of the tire, and an inclination angle xcex2 of the second bent portion inclined with respect to the winding direction of the turnup portion is within a range of 15xcx9c60xc2x0 at the radial section of the tire.
In a further preferable embodiment of the first aspect of the invention, the organic fiber cord layer has the first bent portion, the second bent portion and a third bent portion extending outward from an end of the second bent portion at an approximately equal distance to an outer surface of the tire in the radial direction of the tire.
In another preferable embodiment of the first aspect of the invention, the organic fiber cord layer has the first bent portion and the third bent portion extending outward from the end of the first bent portion at an approximately equal distance to an outer surface of the tire in the radial direction of the tire.
In the other preferable embodiment of the first aspect of the invention, the organic fiber cord layer has the first bent portion, the third bent portion and a fourth bent portion extending from the third bent portion toward the inside of the tire and acutely inclining with respect to the winding direction of the turnup portion.
The inclination angle xcex3 of the fourth bent portion with respect to the winding direction of the turnup portion is within a range of 15xcx9c60xc2x0 at the section of the tire.
In order to achieve the above object, a second aspect of the invention lies in a heavy duty pneumatic radial tire comprising a carcass of at least one rubberized cord ply of radial arrangement toroidally extending between a pair of bead cores embedded in bead portions and wound around the bead core from inside of the tire toward outside to form a turnup portion, at least one bead portion reinforcing layer made of a rubberized steel cord layer extending outside the turnup portion over an end of the turnup portion outward in a radial direction of the tire, in which the organic fiber cord layer is arranged so as to extend from a position near to an outside of the bead core over the end of the bead portion reinforcing layer toward the outside of the tire and spread apart from the bead portion reinforcing layer.
In a preferable embodiment of the second aspect of the invention, the organic fiber cord layer has a first bent portion acutely bending toward the outside of the tire with respect to the bead portion reinforcing layer extending outward from the position near to the outside of the bead core in the radial direction and the extending direction of the bead portion reinforcing layer, and a bending angle xcex1 of the first bent portion with respect to the extending direction of the bead portion reinforcing layer at xcex1 radial section of the tire is within a range of 15xcx9c60xc2x0.
In another preferable embodiment of the second aspect of the invention, an end of the first bent portion of the organic fiber cord layer is an outermost end in the radial direction of the tire.
In the other preferable embodiment of the second aspect of the invention, the organic fiber cord layer has the first bent portion and a second bent portion again bending from an end of the first bent portion toward an inside of the tire, and an inclination angle xcex2 of the second bent portion inclined with respect to the extending direction of the bead portion reinforcing layer is within a range of 15-60xc2x0 at the radial section of the tire.
In a further preferable embodiment of the second aspect of the invention, the organic fiber cord layer has the first bent portion, the second bent portion and a third bent portion extending outward from an end of the second bent portion at an approximately equal distance to an outer surface of the tire in the radial direction of the tire.
In another preferable embodiment of the second aspect of the invention, the organic fiber cord layer has the first bent portion and the third bent portion extending outward from the end of the first bent portion at an approximately equal distance to an outer surface of the tire in the radial direction of the tire.
In the other preferable embodiment of the second aspect of the invention, the organic fiber cord layer has the first bent portion, the third bent portion and a fourth bent portion extending from the third bent portion toward the inside of the tire and acutely inclining with respect to the extending direction of the bead portion reinforcing layer.
The inclination angle xcex3 of the fourth bent portion with respect to the extending direction of the bead portion reinforcing layer is within a range of 15-60 at the section of the tire.
In order to achieve the above object, a third aspect of the invention lies in a heavy duty pneumatic radial tire comprising a carcass of at least one rubberized cord ply of radial arrangement toroidally extending between a pair of bead core embedded in bead portions and wound around the bead core from inside of the tire toward outside to form a turnup portion, and at least one rubberized organic fiber cord layer extending outside the turnup portion over an end of the turnup portion outward in a radial direction of the tire, in which at least a cord layer portion of the organic fiber cord layer located at the side of the turnup portion has a first bent portion bending such that its outer end is inclined toward an inside of the tire in a radial direction thereof.
In a preferable embodiment of the third aspect of the invention, a bending angle xcex8 of the first bent portion with respect to the winding direction of the turnup portion is within a range of 15xcx9c70xc2x0 at the section of the tire.
In another preferable embodiment of the third aspect of the invention, a bead portion reinforcing layer made of a rubberized steel cord layer is disposed between the turnup portion of the carcass and the organic fiber cord layer, and an outer end of the reinforcing layer in the radial direction of the tire locates inward from an end of the turnup portion in the radial direction of the tire.
In the other preferable embodiment of the third aspect of the invention, a bead portion reinforcing layer made of a rubberized steel cord layer is disposed between the turnup portion of the carcass and the organic fiber cord layer, and an outer end of the reinforcing layer in the radial direction of the tire locates between an end of the turnup portion and an outer end of at least the cord layer portion of the organic fiber cord layer located at the side of the turnup portion of the carcass, and the first bent portion located outward from the outer end of the bead portion reinforcing layer in the radial direction of the tire.
In a still further preferable embodiment of the third aspect of the invention, the end of the first bent portion of the organic fiber cord layer is an outermost end in the radial direction of the tire.
In the first, second and third aspects of the invention and their preferable embodiments, it is common that each length of the first bent portion, second bent portion and third bent portion of the organic fiber cord layer is within a range of 4xcx9c50 mm.
In the first, second and third aspects of the invention, the organic fiber cord layer is suitable to be a nylon cord layer.